1. Field of the Invention
The present invention relates to an image reading apparatus for reading images on both sides of a sheet.
2. Description of the Related
When a double-sided original is handled by a conventional image reading apparatus, the following original conveyance/reading mechanisms are used: A mechanism (referred to as "the first example" hereinafter) in which an original is first conveyed for reading an image on the front side, and the original is then turned upside down and again conveyed for reading an image on the back side, and a mechanism (referred to as "the second example" hereinafter) in which a conveyance passage having a length of at least double the length of an original to be read, so that an image on the front side of the original is read in the first half of the conveyance passage, and an image on the back side is then read in the latter half of the conveyance passage.
Another possible double-side reading apparatus is a reading apparatus (referred to as "the third example" hereinafter) of the type in which two image sensors are provided one on each side of a conveyance passage, and one scanning line on the front side of an original is serially connected to one scanning line on the back side for subsequent processing, as disclosed in U.S. Pat. Nos. 5,038,222, 5,126,855 and 5,280,545. This third example has the advantages of simple construction, and high-speed operation.
However, when the image signal processed by the third example is output to the outside, a special format in which image signals of the front and back sides are serially connected on one scanning line is not easily compatible with general processing systems.
In order to use the image signal read by the third example, an image must be read by a batch processing device for reproducing and separating the image stored in a storage medium into images on the front and back sides of an original, again compressing the images if required, and then transmitting the compressed images to a circuit at the next step. Thus, because a large amount of time is required for reading the images, image output to the next step in real time is impossible in reading, and additional memory for temporarily storing image data is required.